As shown in FIG. 20, a conventional sound image localization apparatus includes a head-related transfer function storage unit 901 having head-related transfer functions corresponding to respective positions, a sound image being localized on the basis of a head-related transfer function corresponding to a designated position, a head-related transfer function selecting unit 902 for selecting a head-related transfer function corresponding to a designated position, and a sound image localization processing unit 903 for filtering a sound source signal on the basis of the selected head-related transfer function, and outputting a sound image localizing signal produced through a sound image localization process.
The sound source signal input into the above-mentioned sound image localization apparatus is convolved with a head-related transfer function corresponding to a designated position, and outputted to an acoustic device such as a headphone or speakers as a sound image localizing signal. When the sound image localizing signal is outputted to the acoustic device under the condition that the head-related transfer function H(f) exceeds 0 dB in the range of a peak included in its amplitude component as shown in FIG. 21, the sound image localizing signal may become distorted, and have a distortion called clipping.
In order to solve this problem, the conventional sound image localization apparatus reduces a gain on all frequency range, and utilizes the head-related transfer function which limits the peak frequency range not to exceed 0 dB as shown in FIG. 22. Also, other conventional sound image localization apparatus aims to prevent clipping on sound image localizing signal by applying sound volume compression methods commonly referred to as limiter or compressor.
As an example of a conventional sound processing apparatus, there has been known a circuit for controlling a quality of a sound to be outputted from an acoustic device such as speakers to prevent the sound from being distorted by a clipping distortion (see patent document 1).
Patent document 1: Japanese Public Patent Publication No. 07-059187